Laura (author of r.terraflow) wrote: http://article.gmane.org/gmane.comp.gis.grass.devel/1442 Aleksey Naumov wrote: > (b) BTW, what controls the size of those subwatersheds saved in the > "swatershed" map? (Something similat to "threshold" in r.watershed > may be nice...) Laura: "In Terraflow the watershed of a sink represents the *entire* area that flows into the sink. Basically each sink-watershed represents a bucket in the ground that will fill with water when it rains (long enough). Each sink-watershed is well-defined, and does not depend on the choice of a threshold. Selecting all the sinks in the terrain and computing their watersheds defines a partition of the terrain into sink-watersheds.
In general a watershed can be defined by an outlet point. Depending on how the outlet point is chosen, the watershed is larger or smaller. r.watershed solves a more general problem of partitioning the terrain into watersheds of arbitrary outlets (not necessarily sinks) and of a given (approximate) size. The problem is how to choose the outlets in order to have the watersheds define a partition and have approximately the specified size. This is a different problem that computing flow direction and flow accumulation. r.terraflow does not do that (yet) -- but we are working on extending it with this functionality." hope it helps. Hamish ps- I think it would be nice to write a r.catchment script from r.watershed streams map + r.cost/r.drain + r.report + r.mapcalc/r.patch to connect watershed basins from r.watershed into greater catchment areas. ie convert fractal basin areas to integrated hydrologicaly connected areas. ____________________________________________________________________________________ Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user